Process of Cryogenic CoolingIntroductionCryogenic refrigeration is a term that may be applied to the process of cooling equipment and components to temperatures below 150 K. The net capacity of a cryogenic refrigeration system at a particular temperature is the amount of heat that can be applied to a cold station in the system without warming the station above that particular temperature. The cold station may be a bath of cryogenic fluid, or the cold station may be a conductive surface cooled to the bath temperature to which equipment may be fastened.

Cryogenic refrigeration systems are different from the refrigeration equipment we encounter in our everyday environment. The refrigerants used in cryogenic systems are often helium (He), hydrogen (H2), or nitrogen (N2). Insulation techniques used to minimize heat leaks into the cooled parts of the system. There are a few type of cryogenic cooling which include open-cycle refrigeration and closed-cycle refrigeration systems. This report will touch on a close-cycle refrigeration using helium gas.

Process of Two-stage Refrigeration using Helium GasReferring to the figure in the appendix, the figure in the appendix show a two-stage refrigeration with the supply gas stream from the compressor is split at the refrigerator, with about 1.48 g/s at a pressure of 21 atmospheres (2.13 MPa) going to the CCR drive unit. About 0.12 g/s goes to a pressure regulator and then to the JT loop inlet at a pressure of about 20 atmospheres (2.03 MPa). The GM cycle uses isentropic expansions of helium in combination with displacers and regenerators to achieve low temperatures.

Helium at high pressure (about 21 atmospheres, 2.13 MPa) enters through the inlet valve when the displacers are furthest away from the crosshead. The volume at the cold ends (shown as the bottom ends in Fig. 4-8) of the cylinder containing the displacer and regenerator assemblies are near minimum at this point in time. The volume above the regenerators is near maximum at this point in time. Pressurization of this volume causes heating, and the heat is later stored at the upper or warm ends of the regenerators. The regenerators are made of materials having high specific heat in the temperature ranges appropriate to each stage. The goals of the regenerator designs are to (1) store heat, (2) transfer heat quickly between the helium and the regenerator material, (3) minimize the heat transfer from one end to the other end of the regenerator, (4) minimize the dead volume (void space) thus maximizing the filling factor of the regenerator material, and (5) minimize the restriction through the regenerator material

Using Cryogenic Cooling For Industrial Interest1. Simplicity of cryogenic cooling equipment removes involvement of number of trained personnel and encourages small entrepreneurship.2. Low capital investment which allow easy funding from bank3. Reduced freezing time compared to conventional mechanical freezing